linux-kernel - Re: Discard support (was Re: [PATCH] swap: send callback when swap slot is freed)

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Message-ID: <4A86B42F.4050301@rtr.ca>
Date:	Sat, 15 Aug 2009 09:12:15 -0400
From:	Mark Lord <liml@....ca>
To:	Greg Freemyer <greg.freemyer@...il.com>
Cc:	James Bottomley <James.Bottomley@...senpartnership.com>,
	david@...g.hm, Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Nitin Gupta <ngupta@...are.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-scsi@...r.kernel.org, linux-ide@...r.kernel.org,
	Linux RAID <linux-raid@...r.kernel.org>
Subject: Re: Discard support (was Re: [PATCH] swap: send callback when swap
 	slot is freed)

Greg Freemyer wrote:
>
> What filesystems does your script support?  Running a tool like this
> in the middle of the night makes a lot of since to me even from the
> perspective of many / most enterprise users.
..

It is designed to work on any *mounted* filesystem that supports
the fallocate() system call.  It uses fallocate() to reserve the
free space in a temporary file without any I/O, and then FIEMAP/FIBMAP
to get the block lists from the fallocated file, and then SGIO/ATA_16:TRIM
to discard the space, before deleting the fallocated file.

Tested by me on ext4 and xfs.  btrfs has a bug that prevents the fallocate
from succeeding at present, but CM say's they're trying to fix that.

It will also work on *unmounted" ext2/ext3/ext4 filesystems,
using dumpe2fs to get the free lists, and on xfs using xfs_db there.

HFS(+) support is coming as well.

Not currently compatible with LVM 1/2, or with some distros that use
imaginary device names in /proc/mounts --> I'm working on those issues.

> ps: I tried to pull wiper.sh straight from sourceforge, but I'm
> getting some crazy page asking all sorts of questions and not letting
> me bypass it.  I hope sourceforge is broken.  The other option is they
> meant to do this. :(
..

That's weird.  It should just be a simple click/download,
though you will need to also upgrade hdparm to the latest version.

Cheers
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